1. Technical Field of the Invention
The present invention relates to a method and an apparatus for profile mirror surface grinding simultaneously capable of highly precise profiling process and high quality mirror surface grinding of an ultra-hard material with a high efficiency.
2. Description of the Related Art
A stamping tool with complexity and high precision is essentially required for manufacturing some parts, for example a lead frame of a semiconductor in which an integrated circuit is installed, with similar complexity and high precision. Such a stamping tool should be made by profile grinding of an ultra-hard material. Thus, profile grinding processes are required to be carried out to make not only highly precise profiling, but also highly efficient grinding for mirrors to produce a high quality surface that determines a performance (sharpness, life, etc.) as a stamping tool. However, in the conventional grinding art, it is difficult to realize both shaping with high precision and mirror surface grinding of high quality simultaneously with high efficiency.
So far, a metal bond grindstone with high holding strength has been used for complicated profile grinding processes. In such processes, shaping can be done with high precision, although grinding cannot be done to produce a high quality mirror. Therefore, profiling and grinding processes should be done separately from each other. On the other hand, a thin, sharp grindstone to shape a stamping tool with a pattern of such a narrow width as a lead frame should be shaped in consideration of a change of precision caused by deformation of the grindstone. Therefore, mechanical truing is very difficult to apply.
In other words, the following are problems that arise in the background of separate processes for profile mirror surface grinding in the conventional art: (1) the shape of the grindstone used for complicated profiling processes does not allow shaping in high precision again after wearing-out, because the tip (processing part) of the grindstone is sharply pointed and can be easily blunted by wearing-out; (2) reshaping after wearing-out of the tip part does not maintain the sharpness of the grindstone in the profiling process because of the difficulty of dressing the grindstone.
On the other hand, an electrolytic in-process dressing grinding method (hereafter, ELID grinding method) as a grinding means to realize highly efficient, ultra-precise mirror surface grinding impossible with the conventional shaping art has been developed and published by the present applicants. In the ELID grinding method, the electrically conductive bonding part of a metal bond grindstone is dissolved by electrolytic dressing. An efficient mirror surface grinding for an ultra-hard material is made possible by the grinding method using a metal bond grindstone containing fine grains. Particularly, it is very valuable that the ELID grinding process with dressing means for the metal bond grindstone allows highly efficient and ultra-precise processing.
However, a thin grindstone having a sharply-shaped tip is required for the profiling process of the stamping tool particularly for a narrow width pattern such as a lead frame. Therefore, although applying the ELID grinding method allows a highly efficiently and ultra-precisely processed mirror, the following problem occurs: keeping the shape of tip is very difficult and highly precise shaping is also difficult, because the sharply pointed tip (processed part) of the grindstone is intensively subjected to electrolytic dressing.
Therefore, it is desired to add a shaping function of the metal bond grindstone to the ELID grinding process for realizing both highly precise shaping and high quality grinding with high efficiency.